This invention relates generally to racking mechanisms for electrical power equipment and specifically to a racking mechanism that is easier to manufacture, more reliable in operation and that lends itself to modularization.
In the electrical power distribution field, low voltage circuit breakers, fuse trucks and fused circuit breakers are quite large and are usually mounted on a frame with rollers. They generally require mechanical means, such as levering devices, to engage their primary and secondary contacts with electrical power conductors. The breaker may be separate or fused, i.e. mounted on a fuse truck that includes high current fuses. The breakers, fuse trucks and fused circuit breakers are usually housed in protective cubicles, at the rear of which the high current, low voltage power conductors may be accessed. Since circuit breakers and fuse trucks are heavy, they include rollers for enabling them to be moved among various positions, such as Connect, Test, Disconnect and Remove positions, to permit operation, removal, change of fuses, servicing, testing, etc. The cubicle may include a pair of upstanding cradle arms that define slots that are engaged by levering arms that are attached to the racking mechanism. The levering arms engage the slots in the cradle arms, and rotation thereof causes the circuit breaker, fuse truck, of fused circuit breaker (herein sometimes collectively referred to hereinafter as "circuit device") to be rolled into engagement with the electrical power conductors in the cubicle. All the above is very well known in the art and equipment is available from a number of manufacturers. For example, the Square D Company produces a line of DS type circuit breakers which operate in accordance with the above description. While the circuit device racking mechanism presently available performs well, it is unnecessarily costly and may include many separate parts that are disposed about the circuit device for performing the various interlock functions to assure safe operation, removal and testing. It is also difficult to replace fuses in the above-mentioned fuse trucks and fused circuit breakers. The prior art systems of circuit device installation, removal and testing also do not lend themselves to modularization and the manufacturing and operating efficiencies that are obtainable therefrom.
The above noted deficiencies in circuit devices of the prior art are remedied with the present invention. For example, the normal worm gear drive in the levering mechanism used to move the circuit device among the various positions in the cubicle is expensive and requires high torque levels. With the invention, a very simple drive incorporating a travelling nut and a drive shaft with a conventional acme thread is used with a yoke arrangement for rotating the lever arms to move the circuit device among its positions in the cubicle.
Another improvement over prior art circuit device racking mechanisms is in the indicating mechanism that provides a visual signal to the operator of the device position in the cubicle. With present systems, it is often difficult to determine precisely which of the Connect, Test, Disconnect or Remove positions the device is in and the direction of movement required of the drive nut (with a suitable tool) to bring the device into the desired position. Further, in many prior art circuit device racking mechanisms, the indicating mechanism is a pointer that can easily be bent or can snag an operator's clothing. In accordance with another aspect of the present invention, a position indicator is provided that avoids the problems associated with pointers and which, due to its particular background configuration, enables an operator to rapidly and positively identify the direction of circuit device movement when the drive nut is turned.
In the Square D breaker mentioned above, a shutter arrangement is used to prevent access to the drive mechanism (via a suitable drive tool) unless the breaker is tripped. The shutter is spring biased to a closed position covering the drive nut and is mechanically movable to an open position in which the drive nut is accessible. The prior art shutter (and trip plate and padlock mechanisms) have various interlocks to guard against accidents in installing, removing, testing and servicing of the breaker. The interlocks are located on different portions of the breaker and are not conducive to simplified low cost manufacture and assembly. The invention uses a modular drive and levering arrangement, with the shutter, trip plate and padlocking mechanisms providing the prior art interlocks in a very simple and compact arrangement with a minimal number of parts. Accordingly, the arrangement is not only simpler and more ecomonical than the prior art but is more reliable.
The arrangement of the invention is also modular in that the entire racking mechanism may be readily removed, as a unit, from the circuit device to facilitate servicing of the unit and the changing of fuses, if needed.